Throughout the history of aviation, the materials used have considerably evolved in order to be able to increase their resistance, while at the same time reducing their weight. A specific material which complies with these demands is carbon fiber composite material. As a result of its benefits, the use of composite materials currently reaches up to 50% of the structure of the aircraft.
The fuselage is the main assembly of an aircraft, given that the remaining members forming the aircraft are directly or indirectly connected thereto. The shape of the fuselage varies with the main purpose the aircraft is going to have, hence there are several types of fuselage, such as the truss-type, the monocoque-type, or semi monocoque-type, the latter being the most widely used fuselage type today.
The fuselage of an aircraft comprises members in the form of perpendicular trussing with respect to the longitudinal axis of the aircraft, called frames, which are responsible for giving shape and stiffness to the structure of the fuselage, these frames being placed at intervals in the inner part of the tube of the fuselage of the aircraft. In addition to the frames, the fuselage comprises other reinforcing members, such as the stringers, generally omega-shaped or the like, to optimize the distribution of loads and stiffness. The stringers are placed by connecting the frames along the longitudinal axis of the fuselage, their presence allowing the thinning of the skin of the structure of the fuselage, thus lightening the weight of the assembly of the structure. The stringers in turn perform a secondary reinforcing function, the members being what give shape to the fuselage and forming the main points of connection of the skin. Therefore, the entire framework of frames, stringers and skin are connected to form a complete and stiff structure.
In some areas of the fuselage, it is necessary to make openings, such as passenger doors, cargo doors or windows. In these cases, since the structure of the aircraft is weakened, it is necessary to locally reinforce the area of the opening with other members such as door frames. These members are generically referred to as reinforcing frames.
The fuselage of the aircraft is subjected to all types of structural loads, in addition to also having to withstand the cabin pressurization loads. Overall, the fuselage is subjected to bending, torsional and inertial loads, the pressurization loads mostly being withstood by the skin, the stringers withstanding the bending that the fuselage experiences in the longitudinal direction. In addition, the frames uniformly distribute the loads in each of the segments into which the inner section of the structure of the fuselage is divided, the skin, the stringers and the frames, acting as a single beam, ultimately supporting the torsional and inertial loads.
It would therefore be desirable for current aircraft frames, mainly in the case of heavily loaded structures or frames, to be designed by means of a design providing high stiffness and inertia to the structure, while at the same time not adding weight thereto.
For the case of heavily loaded structures, the profiles forming the frames of the aircraft must comprise strengthening ridges or stiffeners increasing the stiffness of the frames. However, these members increase the total weight of the structure, while at the same time having the drawbacks of eliminating the cleared or useful space inside the structure of the fuselage, this space being very important for purposes of cargo or placing equipment inside large aircraft, while at the same time enormously encumbering the passage of the stringers through the frames, in order to thus connect the same along the longitudinal axis of the fuselage.
The present invention offers a solution to the aforementioned problems.